@mixin square($a) {
  display: block;
  width: $a;
  height: $a;
  line-height: $a;
  text-align: center;
}

@mixin radius($a, $b: 2 * $a) {
  display: block;
  width: $a;
  height: $a;
  line-height: $a;
  border-radius: $b;
  text-align: center;
}
